The development of technical components fulfilling a number of functions increasingly requires the assembly of materials covering the widest possible spectrum of mechanical and physicochemical properties. The present invention relates to composites assembled without resort to adhesives, by using well-known fabricating processes such as overmoulding, two-material injection moulding and coextrusion.
European Application EP 550346 describes a process for obtaining, and articles consisting of, vulcanized rubbers and of polymers containing polyamide blocks which are used in combination without adhesives. It thus becomes possible to combine in the same object the specific properties of rubbers (small residual deformation on compression, low hardness, resistance to abrasion, to hot oils etc.) and the specific properties of polyetheresteramides (flexibility, good mechanical properties, fatigue resistance etc.).
However, the processes employed for producing these objects are partly those of the rubber industry, characterized by long cycle times (typically 10 minutes) and high processing costs.
The objective of the present invention is to obtain composite articles which have the same multiple functions by replacing the part consisting of vulcanized rubber with a thermoplastic rubber (TPV) and by resorting to thermoplastic fabrication processes. It is well known that TPVs are materials which have properties very closely related to vulcanized rubbers while retaining the easy processability of thermoplastics (see the review paper describing these materials by A. Coran et al. in "Thermoplastic Elastomers", MacMillan Publishing 1987).
Patent EP 231674 describes blends consisting of copolymers containing polyamide blocks and nonfunctionalized nitrile rubbers.
Japanese Application JP 63-81158 describes compositions based on polyetheresteramides and on various rubbers which are at least partially crosslinked, the two components being in a ratio of 1:1.
However, in the present invention the advantage of the vulcanization of the rubber lies in the possibility of creating a thermoplastic matrix even if the predominant component is the rubber. The advantage is also that of having a TPV formed by a thermoplastic matrix in which the vulcanized rubber is dispersed. This is valid even if the thermoplastic is in a minority and the rubber in a majority.
In the examples provided by the Japanese Applicant there is only a partial vulcanization of the rubber, whereas an advanced vulcanization (from 50 to 90%) makes it possible to obtain improved properties such as tensile strength, abrasion resistance, better tenacity and residual deformation on compression.